Surgical access system and related methods

ABSTRACT

A surgical access system including a tissue distraction assembly and a tissue retraction assembly, both of which may be equipped with one or more electrodes for use in detecting the existence of (and optionally the distance and/or direction to) neural structures before, during, and after the establishment of an operative corridor to a surgical target site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/058,083, filed Mar. 1, 2016 (now U.S. Pat. No. 9,795,371), which is acontinuation of U.S. patent application Ser. No. 14/287,982, filed May27, 2014 (now U.S. Pat. No. 9,301,743), which is a continuation of U.S.patent application Ser. No. 14/018,209, filed Sep. 4, 2013 (now U.S.Pat. No. 8,747,307), which is a continuation of U.S. patent applicationSer. No. 13/856,648, filed Apr. 4, 2013 (now U.S. Pat. No. 8,602,982),which is a continuation of U.S. patent application Ser. No. 13/756,883,filed Feb. 1, 2013 (now U.S. Pat. No. 8,562,521), which is acontinuation of U.S. patent application Ser. No. 13/466,531, filed May8, 2012 (now U.S. Pat. No. 8,523,768), which is a continuation of U.S.patent application Ser. No. 13/417,499, filed Mar. 12, 2012 (now U.S.Pat. No. 8,343,046), which is a continuation of U.S. patent applicationSer. No. 12/650,301, filed Dec. 30, 2009 (now U.S. Pat. No. 8,133,173),which is a continuation of U.S. patent application Ser. No. 12/636,860(now U.S. Pat. No. 8,403,841), filed Dec. 14, 2009, which is acontinuation of U.S. patent application Ser. No. 10/759,811, filed Jan.16, 2004 (now U.S. Pat. No. 7,691,057), which claims priority to U.S.Provisional Patent Application Ser. No. 60/440,905, filed Jan. 16, 2003,the entire contents of these applications are hereby expresslyincorporated by reference into this disclosure as if set forth fullyherein. The present application also incorporates by reference thefollowing commonly owned patent applications in their entireties(collectively, the “NeuroVision Applications”): PCT App. Ser. No.PCT/US02/22247, entitled “System and Methods for Determining NerveProximity, Direction, and Pathology During Surgery,” filed on Jul. 11,2002; PCT App. Ser. No. PCT/US02/30617, entitled “System and Methods forPerforming Surgical Procedures and Assessments,” filed on Sep. 25, 2002;PCT App. Ser. No. PCT/US02/35047, entitled “System and Methods forPerforming Percutaneous Pedicle Integrity Assessments,” filed on Oct.30, 2002; PCT App. Ser. No. PCT/US03/02056, entitled “System and Methodsfor Determining Nerve Direction to a Surgical Instrument,” filed Jan.15, 2003 (collectively “NeuroVision PCT Applications”).

BACKGROUND OF THE INVENTION I. Field of the Invention

The present invention relates generally to systems and methods forperforming surgical procedures and, more particularly, for accessing asurgical target site in order to perform surgical procedures.

II. Discussion of the Prior Art

A noteworthy trend in the medical community is the move away fromperforming surgery via traditional “open” techniques in favor ofminimally invasive or minimal access techniques. Open surgicaltechniques are generally undesirable in that they typically requirelarge incisions and high amounts of tissue displacement to gain accessto the surgical target site, which produces concomitantly high amountsof pain, lengthened hospitalization (increasing health care costs), andhigh morbidity in the patient population. Less-invasive surgicaltechniques (including so-called “minimal access” and “minimallyinvasive” techniques) are gaining favor due to the fact that theyinvolve accessing the surgical target site via incisions ofsubstantially smaller size with greatly reduced tissue displacementrequirements. This, in turn, reduces the pain, morbidity and costassociated with such procedures. The access systems developed to date,however, fail in various respects to meet all the needs of the surgeonpopulation.

One drawback associated with prior art surgical access systems relatesto the ease with which the operative corridor can be created, as well asmaintained over time, depending upon the particular surgical targetsite. For example, when accessing surgical target sites located beneathor behind musculature or other relatively strong tissue (such as, by wayof example only, the psoas muscle adjacent to the spine), it has beenfound that advancing an operative corridor-establishing instrumentdirectly through such tissues can be challenging and/or lead to unwantedor undesirable effects (such as stressing or tearing the tissues). Whilecertain efforts have been undertaken to reduce the trauma to tissuewhile creating an operative corridor, such as (by way of example only)the sequential dilation system of U.S. Pat. No. 5,792,044 to Foley etal., these attempts are nonetheless limited in their applicability basedon the relatively narrow operative corridor. More specifically, based onthe generally cylindrical nature of the so-called “working cannula,” thedegree to which instruments can be manipulated and/or angled within thecannula can be generally limited or restrictive, particularly if thesurgical target site is a relatively deep within the patient.

Efforts have been undertaken to overcome this drawback, such as shown inU.S. Pat. No. 6,524,320 to DiPoto, wherein an expandable portion isprovided at the distal end of a cannula for creating a region ofincreased cross-sectional area adjacent to the surgical target site.While this system may provide for improved instrument manipulationrelative to sequential dilation access systems (at least at deep siteswithin the patient), it is nonetheless flawed in that the deployment ofthe expandable portion may inadvertently compress or impinge uponsensitive tissues adjacent to the surgical target site. For example, inanatomical regions having neural and/or vasculature structures, such ablind expansion may cause the expandable portion to impinge upon thesesensitive tissues and cause neural and/or vasculature compromise, damageand/or pain for the patient.

This highlights yet another drawback with the prior art surgical accesssystems, namely, the challenges in establishing an operative corridorthrough or near tissue having major neural structures which, ifcontacted or impinged, may result in neural impairment for the patient.Due to the threat of contacting such neural structures, efforts thus farhave largely restricted to establishing operative corridors throughtissue having little or substantially reduced neural structures, whicheffectively limits the number of ways a given surgical target site canbe accessed. This can be seen, by way of example only, in the spinalarts, where the exiting nerve roots and neural plexus structures in thepsoas muscle have rendered a lateral or far lateral access path(so-called trans-psoas approach) to the lumbar spine virtuallyimpossible. Instead, spine surgeons are largely restricted to accessingthe spine from the posterior (to perform, among other procedures,posterior lumbar interbody fusion (PLIF)) or from the anterior (toperform, among other procedures, anterior lumbar interbody fusion(ALT)).

Posterior-access procedures involve traversing a shorter distance withinthe patient to establish the operative corridor, albeit at the price ofoftentimes having to reduce or cut away part of the posterior bonystructures (i.e. lamina, facets, spinous process) in order to reach thetarget site (which typically comprises the disc space). Anterior-accessprocedures are relatively simple for surgeons in that they do notinvolve reducing or cutting away bony structures to reach the surgicaltarget site. However, they are nonetheless disadvantageous in that theyrequire traversing through a much greater distance within the patient toestablish the operative corridor, oftentimes requiring an additionalsurgeon to assist with moving the various internal organs out of the wayto create the operative corridor.

The present invention is directed at eliminating, or at least minimizingthe effects of, the above-identified drawbacks in the prior art.

SUMMARY OF THE INVENTION

The present invention accomplishes this goal by providing a novel accesssystem and related methods which, according to one embodiment, involvesdetecting the existence of (and optionally the distance and/or directionto) neural structures before, during, and after the establishment of anoperative corridor through (or near) any of a variety of tissues havingsuch neural structures which, if contacted or impinged, may otherwiseresult in neural impairment for the patient. It is expressly noted that,although described herein largely in terms of use in spinal surgery, theaccess system of the present invention is suitable for use in any numberof additional surgical procedures wherein tissue having significantneural structures must be passed through (or near) in order to establishan operative corridor.

The present invention accomplishes this goal by providing a novel accesssystem and related methods which involve: (1) distracting the tissuebetween the patient's skin and the surgical target site to create anarea of distraction (otherwise referred to herein as a “distractioncorridor”); (2) retracting the distraction corridor to establish andmaintain an operative corridor; and/or (3) detecting the existence of(and optionally the distance and/or direction to) neural structuresbefore, during and after the establishment of the operative corridorthrough (or near) any of a variety of tissues having such neuralstructures which, if contacted or impinged, may otherwise result inneural impairment for the patient.

As used herein, “distraction” or “distracting” is defined as the act ofcreating a corridor (extending to a location at or near the surgicaltarget site) having a certain cross-sectional area and shape(“distraction corridor”), and “retraction” or “retracting” is defined asthe act of creating an operative corridor by increasing or maintainingthe cross-sectional area of the distraction corridor (and/or modifyingits shape) with at least one retractor blade such that surgicalinstruments can be passed through operative corridor to the surgicaltarget site.

According to one broad aspect of the present invention, the accesssystem comprises a tissue distraction assembly and a tissue retractionassembly, both of which may be equipped with one or more electrodes foruse in detecting the existence of (and optionally the distance and/ordirection to) neural structures during the steps tissue distractionand/or retraction. To accomplish this, one or more stimulationelectrodes are provided on the various components of the distractionassemblies and/or retraction assemblies, a stimulation source (e.g.voltage or current) is coupled to the stimulation electrodes, astimulation signal is emitted from the stimulation electrodes as thevarious components are advanced towards the surgical target site, andthe patient is monitored to determine if the stimulation signal causesmuscles associated with nerves or neural structures within the tissue toinnervate. If the nerves innervate, this indicates that neuralstructures may be in close proximity to the distraction and/orretraction assemblies.

This monitoring may be accomplished via any number of suitable fashions,including but not limited to observing visual twitches in muscle groupsassociated with the neural structures likely to found in the tissue, aswell as any number of monitoring systems. In either situation(traditional EMG or surgeon-driven EMG monitoring), the access system ofthe present invention may advantageously be used to traverse tissue thatwould ordinarily be deemed unsafe or undesirable, thereby broadening thenumber of manners in which a given surgical target site may be accessed.

The tissue distraction assembly is capable of, as an initial step,distracting a region of tissue between the skin of the patient and thesurgical target site. The tissue retraction assembly is capable of, as asecondary step, being introduced into this distracted region to therebydefine and establish the operative corridor. Once established, any of avariety of surgical instruments, devices, or implants may be passedthrough and/or manipulated within the operative corridor depending uponthe given surgical procedure. The electrode(s) are capable of, duringboth tissue distraction and retraction, detecting the existence of (andoptionally the distance and/or direction to) neural structures such thatthe operative corridor may be established through (or near) any of avariety of tissues having such neural structures which, if contacted orimpinged, may otherwise result in neural impairment for the patient. Inthis fashion, the access system of the present invention may be used totraverse tissue that would ordinarily be deemed unsafe or undesirable,thereby broadening the number of manners in which a given surgicaltarget site may be accessed.

The tissue distraction assembly may include any number of componentscapable of performing the necessary distraction. By way of example only,the tissue distraction assembly may include a K-wire, an initial dilator(of split construction or traditional non-slit construction), and one ormore dilators of traditional (that is, non-split) construction forperforming the necessary tissue distraction to receive the remainder ofthe tissue retractor assembly thereafter. One or more electrodes may beprovided on one or more of the K-wire and dilator(s) to detect thepresence of (and optionally the distance and/or direction to) neuralstructures during tissue distraction.

The tissue retraction assembly may include any number of componentscapable of performing the necessary retraction. By way of example only,the tissue retraction assembly may include one or more retractor bladesextending proximally from the surgical target site for connection with apivot linkage assembly. The pivot linkage includes first and secondpivot arms capable of maintaining the retractor blades in a first,closed position to facilitate the introduction of the retractor bladesover the distraction assembly. Thereafter, the pivot linkage may bemanipulated to open the retractor assembly; that is, allowing theretractor blades to separate from one another (preferablysimultaneously) to create an operative corridor to the surgical targetsite. In a preferred embodiment, this is accomplished by maintaining aposterior retractor blade in a fixed position relative to the surgicaltarget site (so as to avoid having it impinge upon any exiting nerveroots near the posterior elements of the spine) while the additionalretractor blades (i.e. cephalad, caudal and/or anterior retractorblades) are moved or otherwise translated away from the posteriorretractor blade (and each other) so as to create the operative corridorin a fashion that doesn't infringe upon the region of the exiting nerveroots. This is accomplished, in part, through the use of a secondarypivot linkage coupled to the pivot linkage assembly, which allows theposterior retractor blade to remain in a constant position while theother retractor blades are moved. In one embodiment, the anteriorretractor blade may be positioned after the posterior, cephalad, andcaudal retractor blades are positioned into the fully retractedposition. This may be accomplished by coupling the anterior retractorblade to the pivot linkage via an arm assembly.

The retractor blades may be optionally dimensioned to receive and directa rigid shim element to augment the structural stability of theretractor blades and thereby ensure the operative corridor, onceestablished, will not decrease or become more restricted, such as mayresult if distal ends of the retractor blades were permitted to “slide”or otherwise move in response to the force exerted by the displacedtissue. In a preferred embodiment, only the posterior and anteriorretractor blades are equipped with such rigid shim elements, which areadvanced into the disc space after the posterior and anterior retractorblades are positioned (posterior first, followed by anterior after thecephalad, caudal and anterior blades are moved into the fully retractedposition). The rigid shim elements are preferably oriented within thedisc space such that they distract the adjacent vertebral bodies, whichserves to restore disc height. They are also preferably advanced asufficient distance within the disc space (preferably past the midline),which serves the dual purpose of preventing post-operative scoliosis andforming a protective barrier (preventing the migration of tissue (suchas nerve roots) into the operative field and the inadvertent advancementof instruments outside the operative field).

The retractor blades may optionally be equipped with a mechanism fortransporting or emitting light at or near the surgical target site toaid the surgeon's ability to visualize the surgical target site,instruments and/or implants during the given surgical procedure.According to one embodiment, this mechanism may comprise, but need notbe limited to, providing one or more strands of fiber optic cable withinthe walls of the retractor blades such that the terminal (distal) endsare capable of emitting light at or near the surgical target site.According to another embodiment, this mechanism may comprise, but neednot be limited to, constructing the retractor blades of suitablematerial (such as clear polycarbonate) and configuration such that lightmay be transmitted generally distally through the walls of the retractorblade light to shine light at or near the surgical target site. This maybe performed by providing the retractor blades having light-transmissioncharacteristics (such as with clear polycarbonate construction) andtransmitting the light almost entirely within the walls of the retractorblade (such as by frosting or otherwise rendering opaque portions of theexterior and/or interior) until it exits a portion along the interior(or medially-facing) surface of the retractor blade to shine at or nearthe surgical target site. The exit portion may be optimally configuredsuch that the light is directed towards the approximate center of thesurgical target site and may be provided along the entire innerperiphery of the retractor blade or one or more portions therealong.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a perspective view of a tissue retraction assembly (in use)forming part of a surgical access system according to the presentinvention;

FIG. 2 is a perspective view illustrating the components and use of aninitial distraction assembly (i.e. K-wire, an initial dilating cannulawith handle, and a split-dilator housed within the initial dilatingcannula) forming part of the surgical access system according to thepresent invention, for use in distracting to a surgical target site(i.e. annulus);

FIG. 3 is a perspective view illustrating the K-wire and split-dilatorof the initial distraction assembly with the initial dilating cannulaand handle removed;

FIG. 4 is a posterior view of the vertebral target site illustrating thesplit-dilator of the present invention in use distracting in a generallycephalad-caudal fashion according to one aspect of the presentinvention;

FIG. 5 is a side view illustrating the use of a secondary distractionassembly (comprising a plurality of dilating cannulae over the K-wire)to further distract tissue between the skin of the patient and thesurgical target site according to the present invention;

FIG. 6 is a perspective view of a retractor assembly according to thepresent invention, comprising a linkage assembly having three (3)retractor blades coupled thereto (posterior, cephalad, and caudal) forthe purpose of creating an operative corridor to the surgical targetsite (shown in a first, closed position);

FIG. 7 is a perspective view of the retractor assembly of FIG. 6 in asecond, opened (i.e. retracted) position according to the presentinvention;

FIG. 8 is a perspective view illustrating a shim introducer introducinga shim element along the interior of the posterior retractor blade suchthat a distal portion (shim extension) is positioned within the discspace;

FIG. 9 is a back view of a shim element according to the presentinvention dimensioned to be engaged with the inner surface of theposterior (and optionally anterior) retractor blade for the purpose ofpositioning a shim extension within the disc space, such as via the shimintroducer shown in FIG. 8;

FIG. 10 is a perspective view of the retractor assembly of the presentinvention with the shim element disposed along the posterior retractorblade according to the present invention;

FIGS. 11-12 are perspective views of the retractor assembly of thepresent invention, wherein an anterior retractor blade is providedcoupled to the linkage assembly via an arm assembly;

FIG. 13 is a perspective view of the retractor assembly of the presentinvention wherein a shim introducer is employed to introducer a shimalong the anterior retractor blade according to the present invention;

FIG. 14 is a perspective view of the retractor assembly of the presentinvention, wherein the anterior retractor blade may be positioned at adifferent vertical level than the posterior, cephalad, and caudalretractor blades according to the present invention;

FIG. 15 is a perspective view of an exemplary nerve monitoring systemcapable of performing nerve monitoring before, during and after thecreating of an operative corridor to a surgical target site using thesurgical access system in accordance with the present invention;

FIG. 16 is a block diagram of the nerve monitoring system shown in FIG.15; and

FIGS. 17-18 are screen displays illustrating exemplary features andinformation communicated to a user during the use of the nervemonitoring system of FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. It is furthermore to be readily understood that,although discussed below primarily within the context of spinal surgery,the surgical access system of the present invention may be employed inany number of anatomical settings to provide access to any number ofdifferent surgical target sites throughout the body. The surgical accesssystem disclosed herein boasts a variety of inventive features andcomponents that warrant patent protection, both individually and incombination.

It is furthermore to be readily understood that, although discussedbelow primarily within the context of spinal surgery, the surgicalaccess system and related methods of the present invention may findapplicability in any of a variety of surgical and/or medicalapplications such that the following description relative to the spineis not to be limiting of the overall scope of the present invention.Moreover, while described below employing the nerve monitoring featuresdescribed above (otherwise referred to as “nerve surveillance”) duringspinal surgery, it will be appreciated that such nerve surveillance willnot be required in all situations, depending upon the particularsurgical target site (e.g. disk space, vertebral body, and/or internalorgan), surgical approach (e.g. lateral, posterior, anterior, and/orpostero-lateral approaches to the spine), and spinal level (e.g.cervical, thoracic and/or lumbar).

The present invention is directed at a novel surgical access system andrelated methods which involve creating and maintaining an operativecorridor to the surgical target site, and optionally detecting theexistence of (and optionally the distance and/or direction to) neuralstructures before, during and/or after this process (including the stepsof distraction and/or retraction). This is accomplished by employing thefollowing steps: (1) one or more stimulation electrodes are provided onthe various distraction and/or retraction components; (2) a stimulationsource (e.g. voltage or current) is coupled to the stimulationelectrodes; (3) a stimulation signal is emitted from the stimulationelectrodes as the various components are advanced towards or maintainedat or near the surgical target site; and (4) the patient is monitored todetermine if the stimulation signal causes muscles associated withnerves or neural structures within the tissue to innervate. If thenerves innervate, this may indicate that neural structures may be inclose proximity to the distraction and/or retraction components.

Neural monitoring may be accomplished via any number of suitablefashions, including but not limited to observing visual twitches inmuscle groups associated with the neural structures likely to found inthe tissue, as well as any number of monitoring systems, including butnot limited to any commercially available “traditional” electromyography(EMG) system (that is, typically operated by a neurophysiologist. Suchmonitoring may also be carried out via the surgeon-driven EMG monitoringsystem shown and described in the following commonly owned andco-pending “NeuroVision Applications” incorporated by reference intothis disclosure above. In any case (visual monitoring, traditional EMGand/or surgeon-driven EMG monitoring), the access system of the presentinvention may advantageously be used to traverse tissue that wouldordinarily be deemed unsafe or undesirable, thereby broadening thenumber of manners in which a given surgical target site may be accessed.

Distraction followed by retraction is advantageous because it providesthe ability to more easily position an operative corridor-establishingdevice through tissue that is strong, thick or otherwise challenging totraverse in order to access a surgical target site. The variousdistraction systems of the present invention are advantageous in thatthey provide an improved manner of atraumatically establishing adistraction corridor prior to the use of the retraction systems of thepresent invention. The various retractor systems of the presentinvention are advantageous in that they provide an operative corridorhaving improved cross-sectional area and shape (including customizationthereof) relative to the prior art surgical access systems. Moreover, byoptionally equipping the various distraction systems and/or retractionsystems with one or more electrodes, an operative corridor may beestablished through (or near) any of a variety of tissues having suchneural structures which, if contacted or impinged, may otherwise resultin neural impairment for the patient.

The present invention involves accessing a surgical target site in afashion less invasive than traditional “open” surgeries and doing so ina manner that provides access in spite of the neural structures requiredto be passed through (or near) in order to establish an operativecorridor to the surgical target site. Generally speaking, the surgicalaccess system of the present invention accomplishes this by providing atissue distraction assembly and a tissue retraction assembly, both ofwhich may be equipped with one or more electrodes for use in detectingthe existence of (and optionally the distance and/or direction to)neural structures.

These electrodes are preferably provided for use with a nervesurveillance system such as, by way of example, the type shown anddescribed in co-pending and commonly assigned NeuroVision PCTApplications incorporated by reference above. Generally speaking, thisnerve surveillance system is capable of detecting the existence of (andoptionally the distance and/or direction to) neural structures duringthe distraction and retraction of tissue by detecting the presence ofnerves by applying a stimulation signal to such instruments andmonitoring the evoked EMG signals from the myotomes associated with thenerves being passed by the distraction and retraction systems of thepresent invention. In so doing, the system as a whole (including thesurgical access system of the present invention) may be used to form anoperative corridor through (or near) any of a variety of tissues havingsuch neural structures, particularly those which, if contacted orimpinged, may otherwise result in neural impairment for the patient. Inthis fashion, the access system of the present invention may be used totraverse tissue that would ordinarily be deemed unsafe or undesirable,thereby broadening the number of manners in which a given surgicaltarget site may be accessed.

The tissue distraction assembly of the present invention (comprising aK-wire, an initial dilator, and a split-dilator disposed within theinitial dilator) is employed to distract the tissues extending betweenthe skin of the patient and a given surgical target site (preferablyalong the posterior region of the target intervertebral disc). Asecondary distraction assembly (i.e. a plurality of sequentiallydilating cannulae) may optionally be employed after the initialdistraction assembly to further distract the tissue. Once distracted,the resulting void or distracted region within the patient is ofsufficient size to accommodate a tissue retraction assembly of thepresent invention. More specifically, the tissue retraction assembly(comprising a plurality of retractor blades coupled to a linkageassembly) may be advanced relative to the secondary distraction assemblysuch that the retractor blades, in a first, closed position, areadvanced over the exterior of the secondary distraction assembly. Atthat point, the linkage assembly may be operated to move the retractorblades into a second, open or “retracted” position to create anoperative corridor to the surgical target site.

According to one aspect of the invention, following (or before) thisretraction, a posterior shim element (which is preferably slideablyengaged with the posterior retractor blade) may be advanced such that ashim extension in positioned within the posterior region of the discspace. If done before retraction, this helps ensure that the posteriorretractor blade will not move posteriorly during the retraction process,even though the other retractor blades (i.e. cephalad, caudal, and/oranterior retractor blades) are able to move and thereby create anoperative corridor. Fixing the posterior retractor blade in this fashionhelps prevent inadvertent contact with the existing nerve roots in theposterior region of the spine. The posterior shim element also helpsensure that surgical instruments employed within the operative corridorare incapable of being advanced outside the operative corridor, yetagain preventing inadvertent contact with the exiting nerve roots duringthe surgery. Once in the appropriate anterior position, the anteriorretractor blade may be locked in position and, thereafter, an anteriorshim element advanced therealong for positioning a shim extension withinthe anterior of the disc space.

The shim elements serve to distract the adjacent vertebral bodies(thereby restoring disc height), to form protective barriers (againstthe migration of tissue into (or instruments out of) the operativesite), and to rigidly couple the posterior and anterior retractor bladesin fixed relation relative to the vertebral bodies. Once the operativecorridor is established, any of a variety of surgical instruments,devices, or implants may be passed through and/or manipulated within theoperative corridor depending upon the given surgical procedure.

FIG. 1 illustrates a tissue retraction assembly 10 forming part of asurgical access system according to the present invention. Theretraction assembly 10 includes a posterior retractor blade 12, ananterior retractor blade 14, cephalad retractor blade 16, and caudalretractor blade 18, all of which are coupled to a linkage assembly 20.Posterior and anterior retractor blades 12, 14 establish an AP (or“width”) dimension of an operative corridor 15. Posterior retractorblade 12 and anterior retractor blade 14 are equipped with shim elements22, 24, respectively (shown more clearly in FIG. 9). Shim elements 22,24 serve to distract the adjacent vertebral bodies (thereby restoringdisc height), form protective barriers (against the migration of tissueinto (or instruments out of) the operative site), and rigidly couple theposterior and anterior retractor blades 12, 14 in fixed relationrelative to the vertebral bodies. Cephalad and caudal retractor blades16, 18 establish and maintain the “height” dimension of the operativecorridor 15. Each retractor blade 12-18 (and optionally the shimelements 22, 24) may be, according to the present invention, providedwith one or more electrodes 39 (preferably at their distal regions)equipped for use with a nerve surveillance system, such as, by way ofexample, the type shown and described in the NeuroVision PCTApplications.

The linkage assembly 20 may be coupled to any number of mechanisms forrigidly registering the linkage assembly 20 in fixed relation to theoperative site, such as through the use of an articulating arm mountedto the operating table. The linkage assembly 20 includes first andsecond arm members 26, 28 hingedly coupled at 30. The cephalad retractorblade 16 is rigidly coupled (generally perpendicularly) to the end ofthe first arm member 26. The caudal retractor blade 18 is rigidlycoupled (generally perpendicularly) to the end of the second arm member28. The posterior retractor blade 12 is coupled to the linkage assembly20 via a pivot linkage 32 (comprising a first arm 34 hingedly disposedbetween the posterior retractor blade 12 and the first arm member 26,and a second arm 26 hingedly disposed between the posterior retractorblade 12 and the second arm 28) such that the posterior retractor blade12 will have a tendency to remain in the same position during theretraction process. According to one embodiment, the anterior retractorblade 14 may be coupled to the linkage assembly 20 via an arm assembly38. FIG. 2 illustrates an initial distraction assembly 40 forming partof the surgical access system according to the present invention. Theinitial distraction assembly 40 includes a K-wire 42, an initialdilating cannula 44 with handle 46, and a split-dilator 48 housed withinthe initial dilating cannula 44. In use, the K-wire 42 and split-dilator48 are disposed within the initial dilating cannula 44 and the entireassembly 40 advanced through the tissue towards the surgical target site(i.e. annulus). Again, this is preferably accomplished while employingthe nerve detection and/or direction features described above. After theinitial dilating assembly 40 is advanced such that the distal ends ofthe split-dilator 48 and initial dilator 44 are positioned within thedisc space (FIG. 2), the initial dilator 44 and handle 46 are removed(FIG. 3) to thereby leave the split-dilator 48 and K-wire 42 in place.As shown in FIG. 4, the split-dilator 48 is thereafter split such thatthe respective halves 48 a, 48 b are separated from one another todistract tissue in a generally cephalad-caudal fashion relative to thetarget site. The split dilator 48 may thereafter be relaxed (allowingthe dilator halves 48 a, 48 b to come together) and rotated such thatthe dilator halves 48 a, 48 b are disposed in the anterior-posteriorplane. Once rotated in this manner, the dilator halves 48 a, 48 b areagain separated to distract tissue in a generally anterior-posteriorfashion. Each dilator halve 48 a, 48 b may be, according to the presentinvention, provided with one or more electrodes (preferably at theirdistal regions) equipped for use with a nerve surveillance system, suchas, by way of example, the type shown and described in the NeuroVisionPCT Applications.

Following this initial distraction, a secondary distraction may beoptionally undertaken, such as via a sequential dilation system 50 asshown in FIG. 5. According to the present invention, the sequentialdilation system 50 may include the K-wire 42, the initial dilator 44,and one or more supplemental dilators 52, 54 for the purpose of furtherdilating the tissue down to the surgical target site. Once again, eachcomponent of the secondary distraction assembly 50 (namely, the K-wire42, the initial dilator 44, and the supplemental dilators 52, 54 may be,according to the present invention, provided with one or more electrodes(preferably at their distal regions) equipped for use with a nervesurveillance system, such as, by way of example, the type shown anddescribed in the NeuroVision PCT Applications.

As shown in FIG. 6, the retraction assembly 10 of the present inventionis thereafter advanced along the exterior of the sequential dilationsystem 50. This is accomplished by maintaining the retractor blades12-16 in a first, closed position (with the retractor blades 12-16 ingenerally abutting relation to one another). Once advanced to thesurgical target site, the linkage assembly 20 may be operated as shownin FIG. 7 to move the retractor blades 12-16 into a second, open or“retracted” position. As one can see, the posterior retractor blade 12is allowed to stay in the same general position during this process,such that the cephalad and caudal retractor blades 14, 16 move away fromthe posterior retractor blade 12. Again, this is accomplished throughthe use of the pivot linkage 32 between the posterior retractor blade 12and the arms 26, 28 of the linkage assembly 20.

At this point, as shown in FIG. 8, the posterior shim element 22 (FIG.9) may be advanced along an engagement slot formed along the interiorsurface of the posterior retractor blade 12 such that the shim extension(distal end) is positioned in the posterior region of the disc space asshown in FIG. 10. To aid in this process, a shim introducer 60 may beprovided, which includes a handle member 62 and an elongate portion 64capable of delivering the shim element 22 along the interior of theposterior retractor blade 12 and thereafter selectively disengaging theshim element 22 so as to remove the elongate portion 64 from theoperative site. As shown in FIGS. 11-12, the anterior retractor blade 14may thereafter be positioned relative to the posterior, cephalad, andcaudal retractor blades 12, 16, 18, respectively, by virtue of the armassembly 38. The anterior shim element 24 may thereafter be advancedalong the anterior retractor blade 14 such that the shim extension(distal region thereof) extends into the anterior region of the discspace as shown in FIG. 13. The end result is shown in FIG. 14, with theretraction assembly 10 of the present invention disposed in positionover a surgical target site.

FIGS. 15-16 illustrate, by way of example only, a surgical system 120provided in accordance with a broad aspect of the present invention. Thesurgical system 120 includes a control unit 122, a patient module 124,an EMG harness 126 and return electrode 128 coupled to the patientmodule 124, and an accessory cable 132 in combination with a handleassembly 136. The handle assembly 136 includes one or more electricalconnectors 130, including (by way of example only) a pin connector 134,a pin connector 138, and a clamping-style connector 135. As shown indotted lines, each of the electrical connectors 130 may be coupled tothe handle assembly 136 and include a manner of establishing electricalcommunications with any of the electrodes 39 provided on the distractionand/or retraction assemblies of the present invention, including theshims 22, 24 (collectively “Surgical Access Instruments”). Byestablishing electrical communication in this fashion, the handleassembly 136 may be employed to selectively apply a stimulation signalto any of the Surgical Access Instruments to detect the presence of (andoptionally direction to) neural structures during and/or after thedistraction and retraction steps of the present invention.

The control unit 122 includes a touch screen display 140 and a base 142,which collectively contain the essential processing capabilities forcontrolling the surgical system 120. The patient module 124 is connectedto the control unit 122 via a data cable 144, which establishes theelectrical connections and communications (digital and/or analog)between the control unit 122 and patient module 124. The main functionsof the control unit 122 include receiving user commands via the touchscreen display 140, activating stimulation, processing signal dataaccording to defined algorithms (described below), displaying receivedparameters and processed data, and monitoring system status andreporting fault conditions. The touch screen display 140 is preferablyequipped with a graphical user interface (GUI) capable of communicatinginformation to the user and receiving instructions from the user. Thedisplay 140 and/or base 142 may contain patient module interfacecircuitry that commands the stimulation sources, receives digitizedsignals and other information from the patient module 124, processes theEMG responses to extract characteristic information for each musclegroup, and displays the processed data to the operator via the display140.

The accessory handle assembly 136 includes a cable 155 for establishingelectrical communication with the patient module 124 (via the accessorycable 132). In a preferred embodiment, each electrical connector 130includes a proximal electrical connector 156 and an electrical cable 157for establishing electrical communication between the handle assembly136 and the electrical connectors 134, 138, and 135. The proximalelectrical connector 156 may be designed to thread and/or snap intoengagement with the distal end 159 of the handle assembly 136. In thisfashion, the Surgical Access Instruments may be quickly and easilycoupled (electrically and mechanically) to the accessory handle assembly136. The pin connectors 134 and 138 may be designed to engage withelectrical mating portions provided on the Surgical Access Instruments,wherein these electrical mating portions are in turn electricallycoupled to the electrodes 39. The distal electrical connector of theclamp-type coupler 135 may include any number of suitable electrode orelectrode regions (including protrusions) on or about the distal (orpinching) ends of the clamp arms 161 forming the coupler 135.Corresponding regions (such as electrodes or electrode regions—includingindentations) may be provided on the Surgical Access Instruments(including K-wire 42) according to the present invention.

In all situations, the user may operate one or more buttons of thehandle assembly 136 to selectively initiate a stimulation signal(preferably, a current signal) from the patient module 124 to one of theelectrical connectors 130, and hence the electrodes 39 on thedistraction and retraction assemblies of the present invention. Bymonitoring the myotomes associated with the nerve roots (via the EMGharness 126 and recording electrode 127) and assessing the resulting EMGresponses (via the control unit 122), the surgical system 120 can detectthe presence of (and optionally the direction to) neural structuresduring and after the distraction and/or retraction according to thepresent invention.

In one embodiment, the monitoring system 120 is capable of determiningnerve presence and/or direction relative to one or more of the K-wire42, dilating cannula 44, split-retractor 48, retractor blades 12-18,and/or the shim elements 22, 24 before, during and/or following thecreation of an operative corridor to a surgical target site. Monitoringsystem 120 accomplishes this by having the control unit 122 and patientmodule 124 cooperate to send electrical stimulation signals to one ormore of the stimulation electrodes provided on these Surgical AccessInstruments. Depending upon the location within a patient (and moreparticularly, to any neural structures), the stimulation signals maycause nerves adjacent to or in the general proximity of the SurgicalAccess Instruments to depolarize. This causes muscle groups to innervateand generate EMG responses, which can be sensed via the EMG harness 126.The nerve direction feature of the system 120 is based on assessing theevoked response of the various muscle myotomes monitored by the system120 via the EMG harness 126.

By monitoring the myotomes associated with the nerves (via the EMGharness 126 and recording electrode 127) and assessing the resulting EMGresponses (via the control unit 122), the surgical access system of thepresent invention is capable of detecting the presence of (andoptionally the distant and/or direction to) such nerves. This providesthe ability to actively negotiate around or past such nerves to safelyand reproducibly form the operative corridor to a particular surgicaltarget site, as well as monitor to ensure that no neural structuresmigrate into contact with the retraction assembly 10 after the operativecorridor has been established. In spinal surgery, for example, this isparticularly advantageous in that the surgical access system of thepresent invention may be particularly suited for establishing anoperative corridor to an intervertebral target site in apostero-lateral, trans-psoas fashion so as to avoid the bony posteriorelements of the spinal column.

FIGS. 17-18 are exemplary screen displays (to be shown on the display140) illustrating one embodiment of the nerve direction feature of themonitoring system shown and described with reference to FIGS. 15-16.These screen displays are intended to communicate a variety ofinformation to the surgeon in an easy-to-interpret fashion. Thisinformation may include, but is not necessarily limited to, a display ofthe function 180 (in this case “DIRECTION”), a graphical representationof a patient 181, the myotome levels being monitored 182, the nerve orgroup associated with a displayed myotome 183, the name of theinstrument being used 184 (e.g. dilating cannula 44), the size of theinstrument being used 185, the stimulation threshold current 186, agraphical representation of the instrument being used 187 (in this case,a cross-sectional view of a dilating cannula 44) to provide a referencepoint from which to illustrate relative direction of the instrument tothe nerve, the stimulation current being applied to the stimulationelectrodes 188, instructions for the user 189 (in this case, “ADVANCE”and/or “HOLD”), and (in FIG. 19) an arrow 190 indicating the directionfrom the instrument to a nerve. This information may be communicated inany number of suitable fashions, including but not limited to the use ofvisual indicia (such as alpha-numeric characters, light-emittingelements, and/or graphics) and audio communications (such as a speakerelement). Although shown with specific reference to a dilating cannula(such as at 184), it is to be readily appreciated that the presentinvention is deemed to include providing similar information on thedisplay 140 during the use of any or all of the various Surgical AccessInstruments of the present invention, including the initial distractionassembly 40 (i.e. the K-wire 42, dilating cannula 44, and split dilator48), the secondary distraction assembly 50, and/or the retractor blades12-18 and/or shim elements 22, 24 of the retraction assembly 10.

The retractor blades 12-18 and the shim elements 22, 24 of the presentinvention may also be provided with one or more electrodes for use inproviding the neural monitoring capabilities of the present invention.By way of example only, it may be advantageous to provide one or moreelectrodes on these components (preferably on the side facing away fromthe surgical target site) for the purpose of conducting neuralmonitoring before, during and/or after the retractor blades 12-18 and/orshim elements 22, 24 have been positioned at or near the surgical targetsite.

The surgical access system of the present invention may be sold ordistributed to end users in any number of suitable kits or packages(sterile and/or non-sterile) containing some or all of the variouscomponents described herein. For example, the retraction assembly 10 maybe provided such that the mounting assembly 20 is reusable (e.g.,autoclavable), while the retractor blades 12-18 and/or shim elements 22,24 are disposable. In a further embodiment, an initial kit may includethese materials, including a variety of sets of retractor blades 12-18and/or shim elements 22, 24 (and extensions 80) having varying (or“incremental”) lengths to account for surgical target sites of varyinglocations within the patient, optionally color-coded to designate apredetermined length.

As evident from the above discussion and drawings, the present inventionaccomplishes the goal of providing a novel surgical access system andrelated methods which involve creating a distraction corridor to asurgical target site, thereafter retracting the distraction corridor toestablish and maintain an operative corridor to the surgical targetsite, and optionally detecting the existence of (and optionally thedistance and/or direction to) neural structures before, during and/orafter the formation of the distraction and/or operative corridors.

The surgical access system of the present invention can be used in anyof a wide variety of surgical or medical applications, above and beyondthe spinal applications discussed herein. By way of example only, inspinal applications, any number of implants and/or instruments may beintroduced through the operative corridor, including but not limited tospinal fusion constructs (such as allograft implants, ceramic implants,cages, mesh, etc.), fixation devices (such as pedicle and/or facetscrews and related tension bands or rod systems), and any number ofmotion-preserving devices (including but not limited to nucleusreplacement and/or total disc replacement systems).

While certain embodiments have been described, it will be appreciated bythose skilled in the art that variations may be accomplished in view ofthese teachings without deviating from the spirit or scope of thepresent application. For example, with regard to the monitoring system120, it may be implemented using any combination of computer programmingsoftware, firmware or hardware. As a preparatory act to practicing thesystem 120 or constructing an apparatus according to the application,the computer programming code (whether software or firmware) accordingto the application will typically be stored in one or more machinereadable storage mediums such as fixed (hard) drives, diskettes, opticaldisks, magnetic tape, semiconductor memories such as ROMs, PROMs, etc.,thereby making an article of manufacture in accordance with theapplication. The article of manufacture containing the computerprogramming code may be used by either executing the code directly fromthe storage device, by copying the code from the storage device intoanother storage device such as a hard disk, RAM, etc. or by transmittingthe code on a network for remote execution. As can be envisioned by oneof skill in the art, many different combinations of the above may beused and accordingly the present application is not limited by the scopeof the appended claims.

What is claimed is:
 1. A method of forming an operating corridor to alumbar spine of a patient, the patient having an anterior aspect, aposterior aspect and two lateral aspects, the method comprising:inserting a first sequential dilator of a plurality of sequentialdilators into the patient at an insertion position on one of the twolateral aspects of the patient and advancing the first sequentialdilator to a lateral aspect of a target intervertebral disc of thelumbar spine, the lateral, trans-psoas path having a path axis thatextends from the insertion position on the one of the two lateralaspects to the other of the two lateral aspects of the patient, whereina first stimulation electrode at a distal region of the first sequentialdilator is configured to deliver electrical stimulation for nervemonitoring, the first sequential dilator comprising a first proximalconnector portion for electrical connection with a nerve monitoringsystem; delivering electrical stimulation signals from the firststimulation electrode while the first sequential dilator is advancedalong the lateral, trans-psoas path to detect and avoid directlycontacting the nerves in the psoas muscle, advancing an elongatepenetration member extending through the first sequential dilator intothe target intervertebral disc, advancing a second sequential dilator ofthe plurality of sequential dilators over the first sequential dilatoralong the lateral, trans-psoas path to the targeted intervertebral discof the lumbar spine; simultaneously delivering a three retractor bladesof a retractor assembly over an outermost dilator of the plurality ofsequential dilators along the lateral, trans-psoas path, wherein thethree retractor blades slide over the outermost dilator of the pluralityof dilators in a closed position in which the three retractor blades areadjacent one another to form an enclosed corridor along the lateraltrans-psoas path to the target intervertebral disc; positioning theretractor assembly such that the three retractor blades comprise aposterior retractor blade, a caudal retractor blade, and a cephaladretractor blade; removing the plurality of sequential dilators fromafter the three retractor blades are positioned along the lateral,trans-psoas path; advancing a shim device along the posterior retractorblade to a position in which a portion of the shim device extends fromthe posterior retractor blade and into the target intervertebral disc;and adjusting the retractor assembly to move the caudal retractor bladeand the cephalad retractor blade away from the posterior retractor bladeto an open position such that the three retractor blades form anon-enclosed operating corridor to the target intervertebral disc of thelumbar spine that is dimensioned to pass an implant; and after adjustingthe retractor assembly to form the operating corridor, passing animplant through the operative corridor along the lateral, trans-psoaspath to the targeted intervertebral disc of the lumbar spine.
 2. Themethod of claim 1, further comprising actuating a blade holder assemblyof the retractor assembly to adjust the retractor assembly from theclosed position to the open position.
 3. The method of claim 2, whereinthe three retractor blades extend generally perpendicularly relative toarm portions of the blade holder assembly.
 4. The method of claim 1,wherein the elongate penetration member is delivered together with thefirst sequential dilator along the lateral, trans-psoas path.
 5. Themethod of claim 4, wherein the elongate penetration member comprises aK-wire.
 6. The method of claim 1, comprising the additional step ofdelivering a fourth retractor blade along the lateral, trans-psoas pathafter adjusting the retractor assembly to the open position and couplingthe fourth retractor blade to the retractor assembly.
 7. The method ofclaim 6, wherein the fourth retractor blade is positioned to be ananterior retractor blade along the lateral, trans-psoas path.
 8. Themethod of claim 1, wherein the shim device includes a proximal portionconfigured to releasably attach to the posterior blade and a distalextension configured to extend distally of the posterior blade andpenetrate into the target intervertebral disc space.
 9. The method ofclaim 8, wherein the proximal portion includes a rearwardly extendingridge structure to releasably engage with a corresponding groove alongan interior face of the posterior retractor blade when the shim deviceis advanced along the posterior retractor blade.
 10. The method of claim10, wherein the shim device has a maximum longitudinal length extendingfrom a proximal-most end of the proximal portion to a distal-most end ofthe distal extension and extending parallel to a longitudinal axis ofthe shim device, wherein the maximum longitudinal length of the shimdevice is less than a maximum longitudinal length of the posteriorretractor blade.
 11. The method of claim 10, wherein the distalextension includes a maximum lateral width located proximally away froma distal-most end of the distal extension, the proximal portion having aproximal lateral width that is greater than the maximum lateral width ofthe distal extension.
 12. The method of claim 11, wherein thedistal-most end of the distal extension includes a tapered tip region.13. The method of claim 1, wherein adjusting the retractor assemblyincludes pivoting a first pivot arm coupled to the cephalad retractorblade and pivoting a second pivot arm coupled to caudal retractor blade.14. The method of claim 1, comprising the additional step of deliveringelectrical stimulation signals from a second stimulation electrode at adistal region of the second sequential dilator the a second firststimulation electrode while the second sequential dilator is advancedalong the lateral, trans-psoas path to detect and avoid directlycontacting the nerves in the psoas muscle, the second sequential dilatorcomprising a second proximal connector portion for electrical connectionwith a nerve monitoring system.
 15. The method of claim 1, furthercomprising: electrically connecting a cable of the nerve monitoringsystem to the first proximal connector portion of first sequentialdilator, wherein the nerve monitoring system delivers an electricalstimulation signal to the first stimulation electrode of the firstsequential dilator during advancement of the first sequential dilatoralong the lateral, trans-psoas path to the targeted intervertebral discof the lumbar spine, the nerve monitoring system monitoring muscleactivity detected by a set of sensor electrodes in communication withleg muscles associated with the nerves in the psoas muscle, and thenerve monitoring system displaying to a user a numeric stimulationcurrent threshold required to obtain the detected muscle activity in atleast one of said leg muscles during advancement of the first sequentialdilator.
 16. The method of claim 15, wherein the muscle activity isdetected with electromyography (EMG) sensors.